Transmission sensor

ABSTRACT

The invention relates to a transmission sensor ( 1 ) for measuring the turbidity of a fluid, comprising a first and a second measuring section ( 2, 3 ). A transmitter ( 6 ) emits electromagnetic radiation into the two measuring sections ( 2, 3 ). A first receiver ( 14 ) is allocated to the first measuring section ( 2 ) and a second receiver ( 15 ) is allocated to the second measuring section ( 3 ). The transmitter ( 6 ) is inserted into a transmitter carrier ( 8 ) in such a way that the transmitter ( 6 ) is forced to adopt a predetermined oriented position. The receivers ( 14, 15 ) are inserted into a receiver carrier ( 18 ) in such a way that each of said receivers ( 14, 15 ) is forced to adopt a predetermined oriented position. A transmitter carrier holder ( 9 ) forcibly positions the transmitter carrier ( 8 ) in a predetermined location and a receiver carrier holder ( 19 ) forcibly positions the receiver carrier ( 18 ) in a predetermined location.

CROSS REFERENCE TO RELATED APPLICATIONS

Applicants claim priority under 35 U.S.C. §119 of German Application No.101 19 932.5 filed on Apr. 23, 2001. Applicants also claim priorityunder 35 U.S.C. §365 of PCT/DE02/01465 filed on Apr. 22, 2002. Theinternational application under PCT article 21(2) was not published inEnglish.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a transmission sensor suitable for measuringturbidity of a fluid. This invention also relates to the use of such atransmission sensor and a method of operation using it.

2. The Prior Art

German Patent Application DE 199 57 592.4 of Nov. 30, 1999 discloses atransmission sensor having a lengthy first measurement zone and ashorter second measurement zone. The two measurement zones are filledwith a fluid, the turbidity of which is to be measured during operationof the sensor. The known transmission sensor has a housing with a wallthat is transparent for electromagnetic radiation, in particular light,at least in the area of the measurement zones. The transmission sensorhas a transmitter, which is arranged in the housing and emitselectromagnetic radiation, in particular infrared light, into themeasurement zones through an inlet area in the wall. A first receiver ofthe transmission sensor is situated in the housing and senses theradiation passing through the first measurement zone through a firstoutlet area in the wall. In a corresponding manner, a second receiver,which is also situated in the housing, senses the radiation transmittedthrough the second measurement zone through a second outlet area in thewall. The known transmission sensor thus has two independent signalpathways or radiation pathways within the fluid, in particular lightpathways, which differ with regard to the path traveled by the radiationbetween the transmitter and the receiver. By comparing the receivedsignals sensed at the receivers, it is possible to determine the degreeof contamination of the fluid, i.e., the turbidity of the fluid.

With the help of such a transmission sensor, a turbidity can be measuredin a fluid in particular, where this turbidity develops when the fluidis mixed, i.e., contaminated with solid foreign matter (suspension)and/or liquid foreign matter (emulsion).

Transmission sensors of this type are used, for example, in oil systemsthat work with hydraulic oils or lubricant oils. For environmentalprotection reasons, hydraulic oils and lubricant oils should be designedto be environmentally friendly, in particular biodegradable. Theserequirements result in oils having a comparatively low stability withrespect to hydrolytic cleavage when they come in contact with water. Inthe case of oils, in particular oils that are capable of rapidbiological degradation, however, even with traditional mineral oils, alow water content therefore contributes greatly to a long oil lifetime.An unacceptably high water content may lead to aging products, inparticular by hydrolysis, and may cause problems with materials andfunctions in equipment that is supplied with and/or working with suchoil. Since water content in oil causes turbidity, in particular in theinfrared range, it is possible to monitor the water content in oil bymeans of such a transmission sensor in order to be able to shut down therespective oil system promptly on reaching a critical water content, forexample.

In such an oil system, a so-called “coalescer” may be provided forelimination of water; a coalescer removes water from oil passing throughit. Since such a coalescer functions like a fine filter, permanent flowthrough the coalescer rapidly leads to clogging due to other noncriticalimpurities entrained by the oil. To prevent such premature clogging ofthe coalescer, the water content in the oil must be measured with thegreatest possible accuracy, so the oil stream passes through thecoalescer only when needed.

A transmission sensor of the type defined in the preamble may also beused in a plurality of other applications. For example, with the help ofsuch a transmission sensor, it is possible to monitor the degree ofcontamination of rinse water in a dishwashing machine or a washingmachine, so that fresh water can be added as a function of this degreeof contamination. This makes it possible to reduce fresh waterconsumption. Furthermore, in the food industry, in particular in thebeverage industry, such a transmission sensor may be used to monitor thequality of the liquid achieved in production. Likewise, the quality ofdrinking water and/or wastewater can be monitored by such a transmissionsensor. In addition to measuring the turbidity in liquids, thetransmission sensor is also suitable for measuring turbidity in gases,e.g., for detection of smoke and/or steam. In particular, such atransmission sensor may be used in a clean room or in an ultraclean roomfor monitoring the dust content in the air.

SUMMARY OF THE INVENTION

The present invention is concerned with the problem of providingpossibilities for ensuring economical production of the transmissionsensor in the case of a transmission sensor of the type defined in thepreamble.

This problem is solved according to this invention by a transmissionsensor having the features of Claim 1.

This invention is based on the general idea of using sensors andreceivers in a respective carrier, where the respective carrier isdesigned so that a predetermined aligned position is necessarilyobtained for the sensor and/or for the receiver. In addition, a holderis provided for this carrier, the holder being designed so that apredetermined position necessarily results for the particular carrier inthe housing. Due to these features, very inexpensive standardcomponents, i.e., diodes or transistors may be used for the transmitterand the receiver. Due to the use of the carriers and the holders, thisensures that these inexpensive components will be positioned more orless automatically within relatively narrow position tolerances in thedesired manner in the sensor when the sensor is assembled, withoutrequiring any particular manual skill. Therefore, production does notrequire any increased care and can easily be automated. These measuresthus lead to a transmission sensor which can be manufactured relativelyeasily and inexpensively by mass production.

Inexpensive transmitters in particular have a relatively greatscattering with respect to the direction of emission of the radiationemitted. Various measures are proposed for reducing the influence ofthese scattering effects on the radiation intensity arriving at thereceivers.

Transmitter aperture arrangements may be connected downstream from thetransmitter to thereby blank out interfering outside ranges of theradiation. Alternatively or additionally, a receiver aperturearrangement may be connected upstream from each receiver to therebyreduce the passage of light scatter to the particular receiver. Such anaperture arrangement may be formed by one aperture or by a flushalignment of a pair of apertures, i.e., by two apertures arranged inalignment with one another, or by a tunnel, a so-called collimator. Inaddition, it has been found that with relatively short measurementzones, scattering effects, in particular a so-called small-anglescattering, have a particularly strong effect. To prevent this, for afurther embodiment it is proposed that any distance between thetransmitter and receiver be designed to be at least approximately tentimes longer than the outlet diameter of the transmitter aperturearrangement allocated to it.

According to an especially advantageous embodiment, the sensor may bedesigned to emit various electromagnetic rays which differ inwavelength. This measure makes it possible to detect a change in colorwithin the fluid, preferably within a liquid, with the help of thetransmission sensor. For example, it is possible in this way to detectcontamination of a first liquid with a second liquid which is soluble init, in particular a liquid of a different color. To this end, a sensormay have a plurality of transmitter elements which generate radiation ofdifferent wavelengths. It is also possible to design a signaltransmitter element so that it can emit rays of different wavelengths.For example, there are known two-color LEDs or duo LEDs which can beswitched between two wavelengths with regard to their light emission.

The transmission sensor according to this invention is suitable in aspecial manner for use in detection of solid and/or liquid impurities ina liquid and for detection of solid and/or liquid impurities in a gas.

The problem on which the present invention is based is also solved by anoperating method having the features of Claim 11. In the inventiveoperating method, a measured value calibration is performed, in which afirst calibration value, which correlates with the intensity of theradiation transmitted through the first measurement zone, and a secondcalibration value, which correlates with the intensity of the radiationtransmitted through the second measurement zone, are determined. Indetermination of a turbidity value which correlates with the turbidityof the fluid, standardized measured values are used. A first measuredvalue, which correlates with the intensity of the radiation transmittedthrough the first measurement zone, and a second measured value, whichcorrelates with the intensity of the radiation transmitted through thesecond measurement zone, are determined first. Then a first standardizedmeasured value is formed by the quotient of the first measured value andthe first calibration value, and a second standardized measured value isformed from the quotient of the second measured value and the secondcalibration value. The turbidity value is then determined on the basisof these standardized measured values.

With the help of this procedure, the condition of the fluid prevailingat the time of calibration of the measured value is defined as thereference condition, so that the turbidity value thus determinedindicates the deviation from this reference condition. This makes itpossible to eliminate the effects of dirt deposits on the transmitterand/or on the receivers, i.e., on the particular wall sections of thesensor through which the radiation passes. Likewise, phenomenaassociated with aging of the transmitter and/or receiver areneutralized. In addition, this neutralizes fluctuations in the outputpower of the transmitters and receivers used, which may occur inparticular in the production of inexpensive electronic components withinmanufacturing tolerances. The method proposed according to thisinvention thus supports the use of inexpensive components.

To determine the turbidity value from the standardized measured values,it is possible to determine, for example, a difference between thestandardized measured values. This difference may then be used to form aturbidity factor, which may be used for additional investigations,tests, controls and regulations. An especially expedient embodiment isone in which a turbidity factor formed by the quotient of the secondstandardized measured value and the first standardized measured value isused to determine the turbidity value which correlates with theturbidity of the fluid.

The problem on which this invention is based is also solved by anoperating method having the features of Claim 14. In this operatingmethod, a transmitter calibration is performed, in which the transmitteroutput power of the transmitter is increased incrementally until apredetermined minimum value for the incoming radiation intensity can bedetected at both receivers. The transmitter output power which thenprevails is used as the operating transmitter output power with whichthe transmitter is operated in determination of a turbidity value whichcorrelates with the turbidity of the fluid. The predetermined minimumvalues mentioned above ensure that an increase in turbidity can still bedetected with certainty on the basis of the starting condition at whichthe transmitter calibration is performed. The incremental increase intransmitter output power ensures that an operating power for thesubsequent measurement operation will be discovered, this operatingpower being just high enough so that an increase in turbidity can bereliably ascertained based on the starting condition which prevails atthe time of calibration of the transmitter. Through these measures, itis usually possible to operate the transmitter at a significantly lowertransmitter output power than the maximum allowed transmitter outputpower of the transmitter. In this way, the lifetime of the transmittercan be increased significantly. The operating method according to thisinvention therefore allows the use of inexpensive transmitters, whichessentially have a short lifetime anyway, but it can be increased to anadequate extent by this invention.

It is clear that the two operating methods according to this inventionfor which patent protection is claimed independently of one another mayalso be implemented cumulatively.

Other important features and advantages of the present invention arederived from the subclaims, the drawings and the respective descriptionof the figures on the basis of the drawings.

It is self-evident that the features mentioned above, which are to bedescribed in greater detail below, may be used not only in theparticular combination given but also alone or in any other combinationswithout going beyond the scope of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred exemplary embodiments of this invention are illustrated in thedrawings and are explained in greater detail in the followingdescription.

The Drawings show schematically:

FIG. 1 a longitudinal section through a transmission sensor according tothis invention;

FIG. 2 a block diagram of a circuit configuration for the transmissionsensor according to FIG. 1;

FIG. 3 a flow chart for a measured value calibration and for atransmitter calibration according to this invention;

FIG. 4 a flow chart for the inventive determination of a turbidityfactor;

FIG. 5 a block diagram for use of a transmission sensor according tothis invention as shown in FIG. 1.

BRIEF DESCRIPTION OF PREFERRED EMBODIMENTS

According to FIG. 1 an inventive transmission sensor 1 has a longerfirst measurement zone 2 and a shorter second measurement zone 3. Duringoperation of the transmission sensor 1, the two measurement zones 2 and3 are filled by a fluid (not shown here), e.g., a liquid or a gas whichis to be monitored for impurities. The transmission sensor 1 has ahousing 4, which has at least one wall 5 that is transparent forelectromagnetic radiation, at least in the area of the measurement zones2 and 3. This housing 4 is preferably manufactured as an injectionmolded part made of plastic.

A transmitter 6, e.g., in the form of a semiconductor element, isprovided in the housing 4 close to an inlet area 7 in the wall 5. Thistransmitter 6 is capable of emitting electromagnetic radiation throughthe inlet area 7 into the measurement zones 2 and 3. The preferredelectromagnetic radiation here is light, in particular infrared light.The transmitter 6 is mounted in a transmitter carrier 8, which isdesigned so that the transmitter necessarily assumes a predeterminedaligned position on insertion into the transmitter carrier 8. Thetransmitter carrier 8 is in turn designed on a transmitter carrierholder 9, which necessarily positions the transmitter carrier 8 in thehousing 4 in a predetermined position in the inlet area 7 by means ofsuitable positioning means. These positioning means may consist, forexample, of an alignment pin 10 and a fitting opening 11, whichcooperates with it. The transmitter 6 is connected at 12 to acircuitboard 13, which carries a circuit for operation of thetransmission sensor 1.

In its housing 4, the transmission sensor 1 also has a first receiver 14and a second receiver 15, which may also be formed by semiconductorelements. While the first receiver 14 is assigned to the firstmeasurement zone 2 and a first outlet area 16 of the wall 5, the secondreceiver 15 is assigned to the second measurement zone 3 and a secondoutlet area 17 of the wall 5. For the two receivers 14 and 15, a commonreceiver carrier 18 is provided, the receivers 14 and 15 being insertedinto corresponding receptacles in this carrier. The receiver carrier 18is designed so that the receivers 14, 15, which are inserted into it,necessarily both assume a predetermined aligned position. A receivercarrier holder 19 is provided for the receiver carrier 18, necessarilypositioning the receiver carrier 18 in the housing 4 in such a way as toresult in a predetermined positioning on the outlet areas 16 and 17 forthe receivers 14 and 15. This receiver carrier holder 19 is necessarilymounted on the circuitboard 13.

The injection mold which is used to manufacture the housing 4 may beequipped with a high-grade planar surface having minimal roughness inthe section which shapes the inlet area 7 and the outlet areas 16 and17, so that the housing 4, which is formed by injection molding, has thesame high-quality surface in these sections of the wall 5.

The transmitter carrier 8 has a first transmitter aperture arrangement20 and a second transmitter aperture arrangement 21 between thetransmitter 6 and the inlet area 7. The first transmitter aperturearrangement 20 is assigned to the first measurement zone 2 and isarranged in a first beam path 22 represented by a broken line.Accordingly, the second transmitter aperture arrangement 21 is assignedto the second measurement zone and is arranged in a second beam path 23,represented by a broken line. Similarly, a first receiver aperturearrangement 24 is also provided on the receiver carrier 18 between thefirst receiver 14 and the first outlet area 16, and a second receiveraperture arrangement 25 is arranged between the second receiver 15 andthe second outlet area 17. The first receiver aperture arrangement 24 isarranged in the first beam path 22 and the second receiver aperturearrangement 25 is arranged in the second beam path 23 accordingly. Eachof the aperture arrangements 20, 21, 24 and 25 is formed here by anaperture and/or a tunnel. If it is assumed that the particular apertureopening is of a negligible extent in the direction of the beam, thenthis is an aperture. However, if it is of an extent with a constantopening cross section in the direction of the beam, it is a tunnel. Anydesired intermediate states are also possible here. As an alternative,the aperture arrangements may each also be formed by a pair of aperturescomprising two apertures positioned in mutual alignment in the directionof the beam, preferably having the same opening cross section.

To reduce the influence of scattering effects, it has been found to beexpedient to have the distances between the transmitters 6 and thereceivers 14, 15 be at least ten times longer than the outlet diameteror opening diameter of the particular assigned transmitter aperturearrangement 20 and/or 21. If both transmitter aperture arrangements 20and 21 have the same outlet diameter, then the shorter secondmeasurement zone 3 should be at least ten times longer than this outletdiameter.

To achieve reproducible, reliable and accurate measurement results, ithas proven to be advantageous to coordinate the lengths of the twomeasurement zones 2 and 3 in such a way that the ratio of the shortersecond measurement zone 3 to the longer first measurement zone 2 has amaximum value of 5:7. A ratio of 5:10 has proven to be optimum.

If the two receivers 14 and 15 are assigned a common transmitter 6 as inthe exemplary embodiment depicted according to FIG. 1, then the two beampaths 22 and 23 intersect at point 26 in the transmitter 6. The firstbeam path here extends from the transmitter 6 to the first receiver 14,while the second beam path 23 extends from the transmitter 6 to thesecond receiver 15.

In the embodiment according to FIG. 1, the different measurement zones 2and 3 are formed by the fact that the wall 5 has a step 27 in the areaof the measurement zones 2 and 3. The wall thickness in the secondoutlet area 17 is accordingly greater than in the first outlet area 16.Due to this design, the arrangement of the two receivers 14 and 15 issimplified. In another embodiment, the wall thicknesses of the twooutlet areas 16 and 17 may be selected to be equal in size, in whichcase an offset arrangement of the receivers 14 and 15 is then possible.

In a lateral area 28 of the wall 5, a third receiver 29 may beaccommodated in the housing 4; the receiver is indicated with brokenlines here and is arranged at the side of the measurement zones 2 and 3.While the first two receivers 14 and 15 sense the radiation transmittedthe measurement zones 2 and 3, the third receiver 29 is able to detectthe radiation scattered in the fluid. This may be advantageous forparticular measurement purposes and applications of the transmissionsensor 1.

For conventional applications of the transmission sensor 1, onetransmitter 6 which emits electromagnetic rays at a certain wavelengthis sufficient, but for other applications in which a change in color ina liquid is to be detected, it may be expedient to design thetransmitter 6 so that it can emit different electromagnetic radiationwhich differs in its wavelength. The transmission measurements are thenperformed at different wavelengths and compared. A change in color inthe fluid may have different effects on the transmission at differentwavelengths. Due to the transmitter 6, which can be switched between atleast two wavelengths, this effect can be used to determine a change incolor.

According to FIG. 2, a circuit 30 for a transmission sensor 1 accordingto FIG. 1 is divided functionally and optionally also physically into anoptical region 31, shown at the top of FIG. 2, and an analysis region32, shown at the bottom of FIG. 2. At least the optical region 31 havingthe measurement zones 2 and 3, the transmitter 6 and the receivers 14and 15 is accommodated in the housing 4 of the transmission sensor 1. Inaddition, a temperature sensor 33 may also be provided, e.g., in theform of an NTC (negative temperature coefficient) resistor, which isused to measure the temperature in the fluid and accordingly is alsosituated expediently on the transmission sensor 1 in or on an areaexposed to the fluid.

The analysis region 32, which may essentially also be situated in thehousing 4 of the transmission sensor 1, e.g., on the circuitboard 13,has an amplifier 34 for the first receiver 14, an amplifier 35 for thesecond receiver 15 and an amplifier 36 for the temperature sensor 33. Acurrent transformer 37 for transforming the current of the transmitter 6is provided for the transmitter 6. The amplifiers 34, 35, 36 and thecurrent transformer 37 are connected to a microprocessor 38. Thismicroprocessor 38 is also connected to a rewritable permanent memory 39,e.g., an EEPROM. In addition, the microprocessor 38 is connected to anoutput driver 40, which signals a turbidity value that has beendetermined and/or signals the operating readiness of the arrangementover output lines 41 and 42. The circuit 30 is connected via a voltagestabilizer 43 and connecting lines 44 and 45 to a power supply. Theindividual current consumers of the circuit 30 are connected to thisvoltage stabilizer 43 by terminals 46.

The microprocessor 38 is also connected to a switch 47 with which thecalibration processes according to this invention, as explained ingreater detail below, can be initialized. In addition, an adjustmentdevice 48 is provided, e.g., a potentiometer, which is connected to themicroprocessor 38 and is used, for example, for setting a limit value oralarm value for the turbidity of the liquid to be tested. Finally, aninterface 49 may be provided so that the microprocessor 38 and/or thecircuit 30 can be connected by this interface to an external analyzerdevice, e.g., a personal computer. In this way, it is possible to plotand analyze the curve of turbidity over time, for example.

FIG. 3 shows a simplified flow chart for implementation of a calibrationprocess according to this invention. This diagram shows a starting point50 for the calibration process. For example, a calibration process isstarted when the switch 47 according to FIG. 1 is operated manually.Likewise it is possible for the microprocessor 38 to trigger the start50 of the calibration process.

In the present invention a distinction is made between a measured valuecalibration and a transmitter calibration. However, it is quite possiblefor these two calibration operations to be performed in a joint combinedcalibration operation. This joint combined calibration operation isdepicted in FIG. 3.

After the start 50, first a value for a calibrated operating transmitteroutput power of the transmitter 6 is set at zero. Since the transmitteroutput power correlates with the current supplied, the transmitteroutput power is indicated below as I; accordingly, the calibratedoperating transmitter output power is I_(cal). In step 51, I_(cal) istherefore set at 0 mA. In a subsequent step 52, in the preferredembodiment depicted here, the prevailing temperature of the fluid isdetermined with the help of the temperature sensor 33. A query 53determines whether the temperature thus detected is a predeterminedminimum temperature which may be, for example, 0° C. when testing thewater content in oil. If the outcome of this query 53 is negative, i.e.,if the prevailing temperature has not reached the required minimumtemperature, an error message is generated at 54 and the calibrationoperation is terminated at 55. The microprocessor 38 may send the errormessage as a signal to the user over the interface 49 and over theoutput driver 40.

If the query 53 has a positive outcome, then in step 56 the calibratedoperating transmitter output power I_(cal) is incremented by a certainamount. For example, the current supplied is increased by 0.2 mA. Thenthere is a query 57, which ascertains whether the instantaneousoperating transmitter output power and/or the respective current I_(ca)is below a predetermined upper limit value, which may be 50 mA, forexample. If the outcome of this query is negative, then the operatingtransmitter output power, i.e., the respective current is too high, so acorresponding error message is generated at 58 and the calibrationoperation is terminated at 55. However, if the outcome of the query 57is positive, the instantaneous operating current and/or the operatingtransmitter output power is below the upper limit value, so the processcontinues with step 59. In this step 59, the transmitter 6 is activatedand operated at the instantaneous operating transmitter output powerI_(cal), i.e., the current set at that instant is supplied. In the caseof this transmitter power I_(cal) at both receivers 14 and 15, theradiation intensity which is detectable there, i.e., the incomingradiation intensity, is measured at both receivers. The first measuredvalue M1 _(cal) detectable at the first receiver 14 is determined andcorresponds to a voltage that can be picked up for example at the firstreceiver 14. The situation is similar for a second measured value M2_(cal). After measuring the radiation intensities arriving at receivers14 and 15, the current for the transmitter 6 is turned off again. Thisprocedure ensures that the transmitter 6 will always receive current andbe operated with current when and only when a measurement is beingperformed. In this way, the lifetime of the transmitter 6 as well asthat of the receivers 14 and 15 is increased. To further reduce theactivity of the transmitter 6 in order to increase component lifetime,the current transformer 27 may operate the transmitter 6 by PWM (pulsewidth modulation).

After determination of the measured values M1 _(cal) and M2 _(cal), aquery 60 ascertains whether a predetermined minimum value for theincoming radiation intensity can be detected at both receivers 14 and15. For example, a signal of 4 volts should be detectable at each of thetwo receivers 14 and 15. If the required minimum radiation intensity isdetectable at only one of the two receivers 14 and 15 or if thepredetermined minimum cannot be detected at both receivers 14 and 15,then the process loops back from the query 60 to the incrementation instep 56 to raise the operating transmitter output power I_(cal) by oneadditional increment. For example, the current supplied is increased by0.2 mA more. This results in an incremental increase in the transmitteroutput power of the transmitter 6 until query 60 obtains the result thatthe predetermined minimum for the incoming radiation intensity has beenreached at both receivers 14 and 15. Thus, if query 60 has a positiveoutcome, a signal or a message can be enabled in step 61 to show that aninitial state for the fluid has been detected such that increasingturbidity due to impurities will be detectable in subsequentmeasurements. In step 62 the instantaneous value of the transmitteroutput power I_(cal) as well as the measured values M1 _(cal) and M2_(cal) measured thereby are stored in memory 39. Then the calibrationoperation is terminated at 55. The transmitter output power determinedin this way is used as the operating transmitter output power I_(cal)for subsequent turbidity measurements. Likewise, the measured values sodetermined are used as calibration values M1 _(cal) and M2 _(cal) whichare used in this invention for standardizing the measured values ofsubsequent turbidity measurements.

The transmitter calibration according to this invention is the procedurefor determining the operating transmitter output power I_(cal). Theinventive measured value calibration consists of determining measuredvalues and defining them as calibration values M1 _(cal) and M2 _(cal)with an initial state which prevails during the calibration operation.

With the help of switch 47, for example, the presence of a sufficientlyclear fluid can then be defined manually, for example, if after addingnew oil to an oil system, it is assumed that the oil is sufficientlyclear. To this extent the actuation of the switch 47 constitutes ahigher-level signal with which the calibration operations describedabove can be initiated.

FIG. 4 shows a flow chart for a signal measurement cycle in measurementoperation of the transmission sensor 1 according to FIG. 1. Thetransmitter 6 is activated at 63, with the transmitter 6 being operatedprecisely at the operating transmitter output power I_(cal) determinedby the calibration. In step 64, the radiation intensity arriving atreceivers 14 and 15 at that instant is determined in each case, a firstmeasured value M1 and a second measured value M2 being generated, eachcorrelating with the corresponding radiation intensity. As soon as thesemeasured values M1 and M2 are available, the transmitter 6 is turned offagain at 65 to thereby increase the lifetime of transmitter 6 andreceivers 14 and 15. In step 66, a standardization of the measuredvalues M1 and M2 determined in step 64 is performed as proposedaccording to this invention with the help of the calibration valuesobtained by calibration. In doing so, a first stabilized measured valueM1 _(standard) is formed by the quotients M1/M1 _(cal), i.e., the firstmeasured value divided by the first calibration value. In a similarmanner, a second standardized measured value M2 _(standard) is generatedby the quotient M2/M2 _(cal) (second measured value divided by thesecond calibration value).

In a subsequent step 67, a turbidity factor f is determined; this isachieved, for example, by forming the quotient M2 _(standard)/M1_(standard). The turbidity factor f may also be formed as follows, forexample: (M2 _(standard)−M1 _(standard))/(M2 _(standard)+M1_(standard)). This turbidity factor f correlates with a turbidity valuewhich in turn correlates with the turbidity of the fluid. In asubsequent step 68, this turbidity factor f can be weighted. Forexample, a check determines whether the turbidity factor f is above orbelow a predetermined limit value. This limit value may be set and/orvaried by the adjustment device 48, for example. In addition, theinstantaneous turbidity factor f may be linked to a time signal at 69 tobe able to record the curve of the turbidity factor f over time. Duringmeasurement operation, this sequence 63 through 69 is repeatedperiodically.

For the case when the turbidity factor f thus determined has reached apredetermined threshold value, then at step 68 or step 69, acorresponding message signal may be generated. Likewise, it is possiblefor this message signal to be generated only when the turbidity factor fthus determined has reached the predetermined threshold value at apredetermined number (e.g., 6) of successive turbidity measurements.Errors due to short-term turbidity fluctuations can be eliminated inthis way.

In a further embodiment, this message signal may activate display means,which are provided in particular on the transmission sensor 1, to theuser, e.g., visually that the predetermined threshold value has beenexceeded. This message, i.e., display should expediently be deactivatedand/or reset only by the user, e.g., manually.

The curve of the turbidity of the fluid over time may be analyzed forexample to differentiate a gradual increase in turbidity from a rapidincrease in turbidity, which is indicative of a disturbance incident.Likewise, it is possible to predict when the particular fluid systemwill have to be shut down for maintenance purposes.

A preferred application of the inventive transmission sensor 1 isdepicted in FIG. 5. FIG. 5 shows an oil system 70, e.g., a hydraulicsystem or a lubricant oil system having essentially any type ofequipment 71, which requires oil. The oil circulated in the oil system70 flows through a loop 72 in which the transmission sensor 1, aswitching valve 73 and a water separation device 74, e.g., a coalescer,are arranged. The transmission sensor 1 is arranged in the loop 72 insuch a way that the circulated oil flows through the measurement zones 2and 3. The transmission sensor 1 measures permanently or periodicallythe impurities accumulating in the oil. Of particular importance heremay be the water content in the oil. A corresponding control unit 75monitors the water content in the oil and communicates with thetransmission sensor 1 in this regard. In addition, the control unit 75is connected to the reversing valve 73. As long as the turbiditydetected by the transmission sensor 1 is below a predetermined upperlimit, the reversing valve 73 is connected so that the oil in the loop72 bypasses the water separation device 74 through a bypass 76. Then theoil does not flow through the water separation device 74. However, assoon as the turbidity detected by the transmission sensor 1 has reachedthe preset upper limit, the control unit 75 reverses the reversing valve73, so that the oil in the loop 72 again flows through the waterseparation device 74. In doing so, the water present in the oil, forexample, is separated into a container 77. The control unit 75expediently reverses the switching valve 73 again when a lower limit forthe turbidity, i.e., the water content has been reached. Due to thisprocedure the lifetime of the water separation device 74 is drasticallyincreased, because oil flows through it only when the water content isto be reduced.

In a particular further embodiment, a second transmission sensor 1 maybe arranged downstream from the water separation device 74 so that withits help, an optimum operating point of the water separation device 74can be established. For example, a coalescer may operate optimally onlyup to a certain volume flow; at a greater volume flow, water maypenetrate through the coalescer. This optimum operating point can beestablished relatively accurately when using a downstream secondtransmission sensor 1, so that the efficiency of the entire installationis increased.

Instead of the water content in the oil, contamination of oil withsolids can also be monitored. For example, the lubricant oil of aninternal combustion engine, in particular in a motor vehicle, may bemonitored with the help of this transmission sensor 1. Of particularimportance here is a form of application in which the transmissionsensor 1 in a fluid system, e.g., and oil system, is connecteddownstream from a filter or an absorber or an adsorber to therebymonitor this separation element for proper functioning. In this way itis possible to detect a decline in separation effect by detecting acorresponding increase in contamination downstream from theseparation-element.

1. A transmission sensor suitable for measuring the turbidity of afluid, having a first measurement zone which is or can be filled with afluid, having a second measurement zone which is shorter than the firstmeasurement zone and likewise is or can be filled with fluid, having ahousing which has a wall that is transparent for electromagneticradiation at least in the area of the measurement zones, having at leastone transmitter which is arranged in the housing and emitselectromagnetic radiation into the measurement zones through an inletarea in the wall, having a first receiver which is arranged in thehousing and senses the radiation transmitted through the firstmeasurement zone through a first outlet area in the wall, having asecond receiver which is arranged in the housing and senses theradiation transmitted through the second measurement zone through asecond outlet area in the wall, having a transmitter carrier in whichthe transmitter is placed, where the transmitter necessarily assumes apredetermined aligned position, having a receiver carrier into which thereceivers are placed, whereby the receivers necessarily assume apredetermined aligned position, having a transmitter carrier holderwhich necessarily positions the transmitter carrier in the housing in apredetermined position at the inlet area, having a receiver carrierholder which necessarily positions the receiver carrier in the housingin a predetermined position at the outlet areas; wherein the wall has astep in the area of the measurement zones such that wall thickness inthe second area is greater than in the first outlet area.
 2. Thetransmission sensor according to claim 1, wherein the transmittercarrier has a first transmitter aperture arrangement assigned to thefirst measurement zone and a second transmitter aperture arrangementassigned to the second measurement zone between the transmitter and theinlet area.
 3. The transmission sensor according to claim 2, wherein atleast one of the aperture arrangements is formed by an aperture or by apair of apertures arranged in alignment or by a tunnel.
 4. Thetransmission sensor according to claim 2, wherein each distance betweenthe transmitter and the receivers is at least approximately ten timeslonger than an outlet diameter of the transmitter aperture arrangementassigned thereto.
 5. The transmission sensor according to claim 1,wherein the receiver carrier has a first receiver aperture arrangementbetween the first receiver and a first outlet area and has a secondreceiver aperture arrangement between the second receiver and the secondoutlet.
 6. The transmission sensor according to claim 1, wherein the tworeceivers are assigned a common transmitter, whereby a linear first beampath extending from the transmitter to the first receiver and a linearsecond beam path extending from the transmitter to the second receiverintersect in the transmitter.
 7. The transmission sensor according toclaim 1, wherein the ratio of the length of the second measurement zoneto the length of the first measurement zone amounts to a value of atmost 5:7 or 5:10.
 8. The transmission sensor according to claim 1,wherein a third receiver is provided, this receiver being arranged atthe side of the measurement zones in the housing and sensing theradiation scattered in the fluid through a side area in the wall.
 9. Thetransmission sensor according to claim 1, wherein the transmitter isdesigned so that it can emit different types of electromagneticradiation which differs in wavelength.
 10. Use of a transmission sensoraccording to claim 1, for detecting solid or liquid impurities in aliquid or a gas.
 11. A method of operating a transmission sensor havinga first measurement zone which is filled by a fluid, having a secondmeasurement zone which is shorter than the first measurement zone and isfilled with fluid, having a housing which has a wall that is transparentfor electromagnetic radiation at least in the area of the measurementzones, having a transmitter for electromagnetic radiation assigned tothe two measurement zones, having a first receiver assigned to the firstmeasurement zone sensing the radiation transmitted through the firstmeasurement zone through a first outlet area in the wall, and having asecond receiver assigned to the second measurement zone sensing theradiation transmitted through the second measurement zone through asecond outlet area in the wall, wherein the wall has a step in the areaof the measurement zones such that wall thickness in the second outletarea is greater than in the first outlet area; and wherein a measuredcalibration is performed in which a first calibration value (M1 _(cal))is determined, this value correlating with the intensity of theradiation transmitted through the first measurement zone and in which asecond calibration value (M2 _(cal)) which correlates with the intensityof the radiation transmitted through the second measurement zone isdetermined and to determine a turbidity value which correlates with theturbidity of the fluid a first measured value (M1) is determined whichcorrelates with the intensity of the radiation transmitted through thefirst measurement zone, a second measured value (M2) that correlateswith the intensity of the radiation transmitted through the secondmeasurement zone is determined, a first standardized measured value (M1_(standard)) is formed by the quotient first measured value (MI)/firstcalibration value (M1 _(cal)), a second standardized measured value (M2_(standard)) is formed by the quotient second measured value (M2)/secondcalibration value (M2 _(cal)), the turbidity value is determined fromthe standardized measured values (M1 _(standard)) and M2 _(standard)).12. The operating method according to claim 11, wherein to determine theturbidity value which correlates with the fluid turbidity, a turbidityfactor (f) is determined, this factor being formed by the quotientsecond standardized measured value (M2 _(standard))/first standardizedmeasured value (M1 _(standard)).
 13. The operating method according toclaim 11, wherein to determine the turbidity value which correlates withthe fluid turbidity, a turbidity factor (f) is determined, this factorbeing formed by a quotient whose dividend is formed from the differencebetween the standardized measured values (M1 _(standard), M2_(standard)) and whose divisor is formed by the sum of the standardizedmeasured values (M1 _(standard), M2 _(standard)).
 14. The methodaccording to claim 11, wherein a transmitter calibration is performed inwhich the transmitter output power of the transmitter is increasedincrementally until a predetermined minimum value for the incomingradiation intensity can be detected at both receivers, whereby thetransmitter output power which then prevails is used as the operatingtransmitter output power (I_(cal)) at which the transmitter is operatedin determination of a turbidity value which correlates with theturbidity of the fluid.
 15. The operating method according to claim 14,wherein the incremental increase in the transmitter output power beginsat a value of zero in the first step.
 16. The operating method accordingto claim 14, wherein an upper limit value is predetermined for theincremental increase in the transmitter output power, and a suitableerror signal is generated when the transmitter output power reaches thisupper limit and the predetermined minimum value for the incomingradiation intensity cannot be detected at one of the receivers at least.17. The operating method according to claim 11, wherein the measuredvalue calibration or the transmitter calibration is performed when thepresence of a sufficiently clear fluid is signaled by a higher-levelsignal.
 18. The operating method according to claim 11, wherein asuitable message signal is generated when the turbidity value or theturbidity factor (f) reaches a predetermined threshold value.
 19. Theoperating method according to claim 11, wherein a suitable messagesignal is generated when the turbidity value or the turbidity factor (f)has reached a predetermined threshold at a predetermined number ofdirectly successive turbidity measurements.
 20. The operating methodaccording to claim 11, wherein the curve of the turbidity value or theturbidity factor (f) over time is determined and analyzed.
 21. Theoperating method according to claim 11, wherein the fluid temperature istaken into account in the measured value calibration or in thetransmitter calibration or in the determination of the turbidity valueor the turbidity factor (f).